Trapped Like a Rat..

I recently did some diddling with traps for a trapped vertical I am deriving and wanted to post some pictures for friends to look at. Personally, I prefer the inductor-and-capacitor type of traps over the coax traps because they are neater (as in cleaner) to build. I make no representations regarding better, more efficient, and so on. I just like hacking off pieces of PVC, wrapping the wire, and paralleling it with a mica cap.

Since I am building a 20m/40m vertical (and may yet add to my growing collections of my 20m/40m dipole antennas), these are built to resonate at around 13.5-14.0 MHz. Unfortunately, the best one (the one with the long- leaded mica cap) resonates at just a pinch under 14.0 MHz so I fear that any antenna made with it will attenuate some part of the 20m signal in the CW band. But, since I am experimenting, I will measure this and see.

I used some small lugs on hand and note that one way to secure the traps to the antenna wire is to drill a hole in the PVC on opposite side of the bolt and nuts used to secure the wire and cap lugs. The wire can be looped through the hole, crimped with zip tie for strain relief, and soldered to the lug. When there's a chance, I will put up some pictures.

For the record, the trap capacitance is 27 pF and the inductance is a shade under 5 uH. Your mileage may vary but, what the hell, a decent hunk of wire, a handful of 27 pF caps (surprisingly cheap on eBay) and wire and -- within days -- you can bloviate with the best of those guys who write the QST articles.

Herewith are the pictures.

A Man with two Watches..

Old proverb: A man with one wristwatch knows what time it is; a man with two watches is never quite sure.

I used to use my scope a Tek 7704A ("Old Betsy") from the 70s and my OHR WM- 2 watt meter alternately whichever one is most convenient when I am building and testing radios. (Sadly, Old Betsy has gone to the "Happy Scoping Ground" and is replaced by "Usrula" -- a 400 MHz fire breathng Iwatsu 7840.)

A couple of points here: I am a dilettante and not a wizard like my friend Dick, WB6JDH, who knows everything and can solve any problem you throw at him. (And, believe me, I have thrown a lot of problems at Dick!) Also, I have old-timey test gear that is wa-a-a-a-y complex -- like my 7704A -- and I don't know how to push the envelope on it but I try to learn. That's the fun part of ham radio.

But, some time past during a spate of building some kits and other projects, I noticed that the WM-2 did not agree with my scope. It got to be annoying so the OHR calibration process was revisited -- but it did not obviate the discrepancy. Some time ago, Marshall Emm, N1FN (SK), and I communicated on the WM-2 re calibration and he assured me that -- in essence -- whatever gets you through the night works just fine for calibration. Obviously, the beauty of the WM-2 was that one could build a reasonably accurate QRP watt meter and calibrate it by looping DC voltage levels through the meter circuit and at each level for the three scales, setting the meter to full scale ensured an accurate RF reading. Marshall's email assured me that using a scope to calibrate the WM-2 was preferable and I found that method far less tedious than setting the pots to the WM-2's manual's cal voltages. Also, Marshall said that the WM-2 manuals cal voltages changed over time owing to the batch of diodes in stock for a kit run. So, you might pick up a WM-2 at a swap and get a manual from a previous production run and you're like the man with two watches.  

 That brings me to the nut of the story: how accurate is the stuff on my bench?

The WM-2 watt meter was one of the best little watt meters going because (1) it was a kit and you can build it and (2) it's reasonably accurate and (3) it covers the 0-100 mW range. The downside is that it is not available anymore as OHR has closed down. But mine is calibrated versus the scope and I use it quite frequently.

Also have one or two Diamond SX-200 (and other models) and find them to be surprisingly accurate. But how do I know this? Well, I checked it against "Old Betsy" and now "Ursula". In fact, I have checked them all against my bench scope and calibrated them (when I can). I am not a metrician nor do I make any pretense at achieving a heavenly degree of accuracy, but a calibrated scope will get you closer than "close enough for government work".

My Bird wattmeter (a gift from my late father) was the purported gold standard in my younger days and I relied on that. There's a great web page on the subject by Adam Farson, AB4OJ, that can be found here. It begins as follows:

Adam goes into how a scope can be used to measure RF power from the peak-to- peak voltage (Vpp) of a signal displayed on an oscilloscope and his calculation of power from Vpp borders on a derivation so I will confine the formula I discovered in one of Wayne Burdick's Wilderness Radio creations -- I think it was the Sierra. Wayne says, simply:

So, when I found my Tek 7704A annoyingly out of sync with my WM-2, I bailed on the OHR calibration routine (using the test loop voltage values) and set it against what my scope told me. By using an FT-817 at 30 meters (10,100 Kc; middle of 2-30 Mc HF band) as a power source. The 5.0, 2.5, and 1.0 watt levels can be used for the 10-watt range and the 1.0 and 0.5 watt levels can serve to calibrate the 1-watt range. For the 100 mW range, I used an attenuator in series on the 0.5 watt level. See the table below for mine.

The last four were obtained by means of feeding the 0.5 watt output into an attenuator and knocking the signal down to levels that allow the WM-2 to be "spot checked" on the 100 mW range. Note that none are close to the actual scale markings so they have to be "eyeballed". (This is, in fact, true of the 10 watt and 1 watt range as well.) However, an eyeball approximation was far better than the inaccuracy the WM-2 displayed by using the voltage/test loop method. Here's the attenuator setup:

The last four were obtained by means of feeding the 0.5 watt output into an attenuator and knocking the signal down to levels that allow the WM-2 to be "spot checked" on the 100 mW range. Note that none are close to the actual scale markings so they have to be "eyeballed". (This is, in fact, true of the 10 watt and 1 watt range as well.) However, an eyeball approximation was far better than the inaccuracy the WM-2 displayed by using the voltage/test loop method. Here's the attenuator setup:

The last four were obtained by means of feeding the 0.5 watt output into an attenuator and knocking the signal down to levels that allow the WM-2 to be "spot checked" on the 100 mW range. Note that none are close to the actual scale markings so they have to be "eyeballed". (This is, in fact, true of the 10 watt and 1 watt range as well.) However, an eyeball approximation was far better than the inaccuracy the WM-2 displayed by using the voltage/test loop method. Here's the attenuator setup:

The last four were obtained by means of feeding the 0.5 watt output into an attenuator and knocking the signal down to levels that allow the WM-2 to be "spot checked" on the 100 mW range. Note that none are close to the actual scale markings so they have to be "eyeballed". (This is, in fact, true of the 10 watt and 1 watt range as well.) However, an eyeball approximation was far better than the inaccuracy the WM-2 displayed by using the voltage/test loop method. Here's the attenuator setup:

I happened to score that Telonic attenuator at a swap meet for $10 and it is immaculate as well as dead balls on. But you have to be careful with the power input as more than a watt will probably fry the unit.

Incidentally, much earlier on I discovered the dirty little secret that the Bird watt meter slugs can become notoriously inaccurate and are not to be trusted. When it was discovered that my HF 50 watt and 100 watt slugs were all over the map, I followed the procedures outlined in several videos of which WB9FOL's is typical.

I pried open my two slugs and found that the pot had wandered off value bit but could be adjusted and I did so scaling them against the scope for lower power values. It was then that I noticed that the Diamond SX-200s were surprisingly accurate at low power and I used them to scale the two bird slugs up to the 100 watt level on my IC-706MKIIg and IC-7200 rigs.

There are, of course, methods to "reduce" or divide higher levels of power so they can be measured by a scope. These are merely extensions of the attenuator in the scope and the 10:1 probe but huskier. In fact, AB4OJ includes the principles for one in his write-up:

But, by reputation and use, the SX-200 and similar models are very accurate ballpark references. (I know, I know..) The scaling is as good as the WM-2 and these will handle up to 200 watts.

..as I said, close enough for government work.

Post Script: Here is a handy Vpp to Power conversion chart for 2 Vpp intervals up to power in watts.

One Watter: Watt's up?

Just so you don't think my workbench is orderly and immaculate all the time..

I was closing in on the finish and had added the final amp and output bandpass filter (actually completing the build) and was testing/aligning the radio when I hit a bump in the road. Try as I would setting the output power to one watt, I could not goose the little beast over 0.7W out. I peaked the bandpass filter over and over again. I check out the parts, solder joints, etc. but could not budge the output power past that level..

..at least that's what my OHR WM-2 watt meter was telling me.

"My OHR telling me it's only 0.5W out."

But my trusty, rusty 7704 sang a different tune:

Consulting with my arch-friend, WB6JDH, and doing a little research, I came across a tour de force slide presentation entitled Math for the General Class Radio Operator that N9XH did for the ARRL and those sources cleared a lot up for me. Here are four salient slides from that presentation, right in the wheelhouse with respect to addressing this situation. They are self-explanatory:

So, extrapolating from the above,

(1) Determine total peak-to-peak volts:

4.8 divisions x 5 volts per division = 24 volts peak-to-peak

(2) Convert from peak-to-peak to RMS:

24 volts peak-to-peak / 2 = 12 volts peak x 0.7070 = 8.484 volts RMS

(3) Now solve I = E/R for I (current in amps):

I =  8.484/ 50 ohms = 0.16968 amps

(4) Now solve for P = I x E (power in watts):

P = 8.484 x 0.16968 = 1.440 watts

But Dick simplified this by using .3535 (half of 0.7070) and skipping the determination of the current and squaring the voltage. I will leave you to derive that, but it works out the same:

(1) 24 volts peak-to-peak x 0.3535 = 8.484 volts RMS
(2) 8.484 RMS volts squared = 71.918
(3) 71.978 / 50 ohms = 1.440 watts

Although it is good to know the derivation, I am going with Dick's method as it is shorter and handheld calculator friendly. 

Anyway, however you run the numbers, it works out to 4 divisions being damned close to 1 watt. (About 0.996 watts, actually.)

Now here's the rub. I went back and re-ran the calibration on my OHR WM-2 and it *still* came out around 0.7 watts when the 1-Watter output was set to 4 divisions (20 volts peak-to-peak) on the scope and I cannot explain away the difference. Trying a couple of other watt meters I had in on the bench, I found a some were "inaccurate", but a Diamond SX-200 was "dead on".

I guess it's why I call this "the man with two watches" syndrome. You know - a man with one watch knows what time it is; a man with two watches is never quite sure.

Failing a plausible explanation for the differences and trusting in my scope (a calibrated Tektronix 7704) as being the most accurate source -- AND since my other measurements of various circuit points on my 1-Watter substantially agree with those presented in K7QO's Phase 8 and Phase 9 videos, I deemed that the standard. And, actually, went back to calibrate the OHR WM-2 using the 1-Watter as a reference.

Now, here's an interesting factoid in this which lends to the mystery. About four weeks ago -- sometime around the first part of December 2015 -- wanting to give QRPp (QRP operation at one watt or less) a try, I got out my old NorCal 40A and set it to one watt using the OHR WM-2! Going back and measuring the NorCal 40A with the same WM-2 used to set it to one watt out, I got a similar 0.7 watt output reading. Netiher the WM-2 nor the NorCal 40A was touched in the interim.

Strange, huh?

Anyway, my final pronouncement on the 15 Meter 1-Watter is that it is a fun kit, very reasonably priced, and with Chuck and Diz's documentation, and excellent source of knowledge for the builder who wants to be much more than an appliance operator or "Baofeng Tech".

"Who knows what evil lurks in the heart of.."

"I do, old son.."

One Watt, a ton of fun..Phase One

This post was rescued from my original original blog. It's when I caught the One-Watter building Jones. That was a little radio designed by Diz, W8DIZ, of Kits & Parts and CHuck Adams in support of a code practice course Chuck was doing for folks in Arizona (or so I am told). The idea was to build this litte one watt radio tha the students could take to class and practice sending to one another. Good in theory but the fact was that they were getting some pretty decent DX with the radios and, soon, Diz made the kits available to the hamming public. I fell in love with them after I bought and built my first one for 15 meters. Soon, I was on to a 30m, then 20m, then..then..then 160m! They had a VXO that covered 2 Kc around the various bands' QRO CW watering holes but the rigs grew so popular for the 20m band that Diz developed a "stretch" version that covered from 14.000 Mc to 14.060 Mc. Still have a stretch kit on the shelf plus 40m one that go along with the other kits I stocked up on prior to my retirement in October 2017. Anyway, on to the show..

Started out this project by organizing my work area to implement Chuck's methodology. He likes to mark a full-page schematic as he installs parts and I opted to do the same. In addition, Diz's kits uses the infamous 1/8th watt resistors and my eyes are becoming too feeble to discern colors -- even to the point where my magnifiers will not help. (See the problems I had with the resistors in the Sawdust Regen kit in the previous post.) Consequently, I found the cheapie Chinese component tester I got some months ago to be an indispensable tool for identifying resistors. Guessing that device will never leave my side for future projects.

As Chuck explained in the video above, Phase One consists only of ensuring that 12 volts negotiates the reverse-polarity 1N4007 diode and arrives at the proper pin of the LM396 socket. Also, the LM386 audio amplifier circuit is checked out to see if it working. I was skeptical of this because of my experience with the QST version of the WBR regen receiver and Chuck's comment about the speaker volume being faint. However, I was pleasantly surprised that the circuit provided a lot of volume and am led to believe that the unit will be perfectly suitable for unamplified speakers when put into operation. Pictures below:

Workplace. Not as gloomy as it seems just the flash didn't fire. Note component tester.

Phase One completed with audio circuit.

Audio section.

Radial 100 nF cap substituted for 100 nF SMT cap at C36.

Close up of same. Solder flux has been cleaned away. Cap will be lain flat when board completed.

Phase One schematic progress. Note R12 installed to facilitate C36 replacement.

I would add these notes to my Phase One effort: pay special attention to where Chuck says to go ahead and install ALL of the the SMT caps first if you want to. He mentions it and I pestered Diz who confirmed that installation of same would not adversely affect the "Build and Test" paradigm. Also, note Diz's correction in the addendum (and my pictures above) wherein he recommends NOT installing the C36 SMT cap but rather putting in the axial cap from one of the C36 pads to ground. I asked Diz about this and he says that there was an error in the PCBs dated 09/03/2015 ~~ see the "20150903" below the DC connector holes in the upper right. To quote Diz:

Hi Bill,

Take a look at C36 on the schematic....it connects from ground to the gates of Q8/Q9. Now look at the PCB...it connects C36 from the gates of Q8/Q9 to pin 4 of U4.

The PCB is in error...also known as a royal screw up. Easiest way around the error is to solder an axial 100 cap on the bottom of the PCB. The PCBs is error are silk screened with 20150903.

See http://kitsandparts.com/1watter15u.php

Any PCBs after 20150903 are corrected.

See http://kitsandparts.com/1watter30u2.php

73, Diz, W8DIZ

Parting comment on the LM386 audio amp circuit: I had a spare LM386 N3 rattling around on the bench from my WBR effort and plugged that in when doing Chuck's audio test. (I was too lazy to go rooting around in the kit parts bag.) The audio -- with headphones -- was more than adequate. When I swapped in Diz's kit-provided LM386 N4, it was almost ear-splitting. Again, this leads me to believe that this little rig will perform just fine with in a room with a speaker -- provided the room is not Carnegie Hall.

Anyway, all seemed to check out just fine. On to Phases Two and Three.

One Watter: Phases Two and Three

..I continue my build of the 15 meter One Watter by Diz and Chuck Adams..

Phases Two and Three
I have taken Chuck's Phase Two and Phase Three and combined them into this post. Basically, he has you build then keyer circuit and install and test the chip. Additionally, the transmit keying circuit and receiver muting circuits are tested.

Project schematic completion.

Audio and keyer circuits.

Whole board including the keyer circuit and muting circuit.

Phases Two and Three
While these two phases sound impressive and you'd figure that the testing would be extensive but it's really quite simple. Here, Chuck powers up the board WITHOUT a new chip inserted in a newly built section and tests for the proper DC voltage at the appropriate IC socket pin. This is also important because there are three types of voltage regulators in this project: a 78L05 for the audio circuit, two 78L08s for the receiver mixer and transmitter, and a 78L10 for the VXO and it allows you to double check that the regulators are installed in the proper places.

The Phase Three checkout involves setting the keyer into straight key mode and then keying the unit and measuring various places around the board to see it the keying circuit sends +12 volts when keyed.

Up next is Phase Four which tests the newly constructed demodulator to see if you can get an 8,064 kHz signal through U6 into the audio chain.

One Watter: Phase Four through Phase Eight..

I didn't necessarily blast through the middle and ending phases but I did not document them as thoroughly as I should have. (In fact, I did not document the first phases that completely either. Pretty much a bunch of pictures with comments. But then again, I did so for the following reasons:

 (1) I was lazy.

 (2) I was absorbed in the building process.

 (3) I was learning as much as I could.  (4) Chuck Adams did a better job than I could ever do.

So here's up to Phase Eight -- the driver stage. Everything up through this stage checked out fine and I was set to sail through the last stage (the final and the output bandpass filter) when I hit a bump which I will describe in a final post. However, the bottom line was that the rig ultimately passed with flying colors and is waiting for a home.

So here's some pictures and comments for the last phases.

The T5 transformer on the 15m 1-Watter is wound on a BN-43-2402 binocular core and is actually pretty simple once one realizes that a complete turn is one pass through BOTH holes. (It is, therefore, possible to do a half turn.) If you follow the instructions re wire size and wind the 8-turn secondary first, it's a piece of cake.

T5 wound and ready to go. This one looks like the alien in Independence Day, don't it?

T5 in situ..

T5 ..ibidem..

Left is T4 (VXO circuit) and L1 or L2 (output bandpass filter). (They are identical).

Here is T4 along with L5 in the VXO circuit. Note L5 (left) was wound with 40 turns.

The primary windings of T2 and T3. They require a 1-turn loop for this secondaries.

The whole board just before adding the driver and final stages.

TThe completed driver stage with T1 in place. Note that this is an FT-37-61, the dull grey toroid.

The tricky part is adjusting the pre-driver bandpass filter -- between C23 and C24 but that is only marginally nigglesome to adjust. For the transformers in this stage. Diz recommends an alternative of stripping the entire length of the one-turn secondary for each of these transformers but I opted to use semi-long pieces of bare clipped component leads I had lying around. They were more riggid and saves me the work of tinning, etc.

Also, be sure you get T1 and L4 wound on the correct core. T1 is wound on the FT37-61 core which is dull grey. L4 is wound on an FT37-43 which is blacker and more shiny.

..on to my final adventure!

Let's Kick This Pig!

I am picking this up from where my old blog -- The Right Hand of Zod - off. It was tied to a political blog I did and, a short time afterwards, I shared the blogspot site with a friend. After some period of disuse, he informed me that he wanted to use the site but I could not seem to separate my two blogs from his one, so I just left it. It's there for reference -- The Right Hand of Zod -- and there's some good stuff on it but it is a derelict -- like the Nostromo in Aliens drifting in the void of space. Eventually all of that will either be rescued and brought here or I will put it into an archive of .pdf files for my own memories!